U.S. patent application number 12/720876 was filed with the patent office on 2010-09-30 for solid electrolytic capacitor.
This patent application is currently assigned to SANYO ELECTRIC CO., LTD.. Invention is credited to Nobuhiko Hayashi, Takashi UMEMOTO.
Application Number | 20100246100 12/720876 |
Document ID | / |
Family ID | 42783953 |
Filed Date | 2010-09-30 |
United States Patent
Application |
20100246100 |
Kind Code |
A1 |
UMEMOTO; Takashi ; et
al. |
September 30, 2010 |
SOLID ELECTROLYTIC CAPACITOR
Abstract
A solid electrolytic capacitor includes at least one capacitor
element in which the other end of an anode lead extends beyond an
exposed portion of an electrolyte layer exposed from a cathode
layer. The solid electrolytic capacitor further includes: an anode
terminal connected to the other end of the anode lead, a cathode
terminal connected to the cathode layer, a resin layer and a resin
outer package covering the capacitor element and the resin layer.
The resin layer covering the exposed portion of the electrolyte
layer, the other end of the anode lead, and a connecting part
between the other end of the anode lead and the anode terminal. The
resin layer includes a first resin layer covering the exposed
portion and a second resin layer covering the first resin layer,
the first resin layer being softer than the second resin layer.
Inventors: |
UMEMOTO; Takashi;
(Hirakata-city, JP) ; Hayashi; Nobuhiko;
(Osaka-city, JP) |
Correspondence
Address: |
MOTS LAW, PLLC
1629 K STREET N.W., SUITE 602
WASHINGTON
DC
20006-1635
US
|
Assignee: |
SANYO ELECTRIC CO., LTD.
Morguchi-city
JP
|
Family ID: |
42783953 |
Appl. No.: |
12/720876 |
Filed: |
March 10, 2010 |
Current U.S.
Class: |
361/535 |
Current CPC
Class: |
H01G 9/15 20130101; H01G
9/012 20130101; H01G 9/08 20130101 |
Class at
Publication: |
361/535 |
International
Class: |
H01G 9/08 20060101
H01G009/08 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 31, 2009 |
JP |
2009-084892 |
Claims
1. A solid electrolytic capacitor including at least one capacitor
element that includes an anode, a dielectric layer covering the
anode, an electrolyte layer covering the dielectric layer, a
cathode layer partly covering the electrolyte layer and an anode
lead one end of which is joined to the anode and the other end of
which extends beyond an exposed portion of the electrolyte layer
exposed from the cathode layer, wherein the solid electrolytic
capacitor further includes: an anode terminal connected to the
other end of the anode lead, a cathode terminal connected to the
cathode layer, a resin layer and a resin outer package covering the
capacitor element and the resin layer, wherein the resin layer
covering the exposed portion of the electrolyte layer, the other
end of the anode lead, and a connecting part between the other end
of the anode lead and the anode terminal; and the resin layer
includes a first resin layer covering the exposed portion and a
second resin layer covering the first resin layer, the first resin
layer being softer than the second resin layer.
2. The solid electrolytic capacitor according to claim 1, wherein
the other end of the anode lead and the anode terminal are
connected to each other through a connecting member, and a
connecting part between the other end of the anode lead and the
connecting member is covered with the resin layer.
3. The solid electrolytic capacitor according to claim 1, wherein
the first resin layer covers the entire surface of the exposed
portion.
4. The solid electrolytic capacitor according to claim 1, wherein
the penetration of the first resin layer is within the range of 30
to 200.
5. The solid electrolytic capacitor according to claim 1, wherein a
third resin layer is formed to cover the cathode layer.
6. The solid electrolytic capacitor according to claim 2, wherein
the resin layer covers a connecting part between the connecting
member and the anode terminal.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to solid electrolytic capacitors
having a resin outer package.
[0003] 2. Description of Related Art
[0004] FIG. 17 shows in cross section the structure of a
conventional solid electrolytic capacitor.
[0005] As shown in the figure, a conventional solid electrolytic
capacitor 120 has a capacitor element 106 that includes: an anode
101 made of a valve metal; an anode lead 102 provided in the anode
101 and having one end 102a embedded in the anode 101 and the other
end 102b extending from the anode 101; a dielectric layer 103
formed by anodizing the anode 101; an electrolyte layer 104 formed
on the dielectric layer 103; and a cathode layer 105 formed on the
electrolyte layer 104. The anode 101 and the anode lead 102 are
joined and integrated together by embedding the anode lead 102 into
a powdered mass of a valve metal to extend the other end 102b of
the anode lead from the powdered mass, pressing the powdered mass
into the shape of an anode 101 and sintering it.
[0006] Furthermore, an anode terminal 107 is attached to the other
end 102b of the anode lead 102, and a cathode terminal 109 is
attached to a surface of the cathode layer 105 with a conductive
adhesive 108. The solid electrolytic capacitor 120 is formed
through a molding process including: setting of the capacitor
element 106 in a mold for resin molding with the anode terminal 107
and cathode terminal 109 fixed; and encapsulation with a resin
outer package 111. In this molding process, a resin for forming the
resin outer package 111 is poured into the mold for resin
molding.
[0007] In such a solid electrolytic capacitor 120, the anode 101
and the anode lead 102 are joined and integrated together. In
joining the anode 101 and the anode lead 102, defects and strains
are likely to be produced particularly in the anode 101. The
dielectric layer 103 is a self-oxidation film formed by anodizing
the anode 101. Therefore, if anodization is done with defects or
strains produced in the anode 101 as above, defects or strains are
also likely to be produced in a part of the dielectric layer 103
located in the vicinity of the region in which the anode 101 and
the anode lead 102 are joined together. In addition, the part of
the dielectric layer 103 in the vicinity of to the region in which
the anode 101 and the anode lead 102 are joined together is
susceptible to stress transmitted from the anode lead 102 in the
molding process, whereby the dielectric layer 103 is likely to
produce defects, such as cracks.
[0008] A technique for coping with the above problem is disclosed
in Published Japanese Patent Application No. 2001-203128, in which
a root 102c of the anode lead 102, which is a part at which the
other end 102b of the anode lead extends from the anode, is covered
with a thermosetting resin to hold the anode lead rigidly.
According to this technique, stress applied from the anode lead to
the dielectric layer in the molding process can be reduced.
Therefore, in the solid electrolytic capacitor disclosed in the
above document, the occurrence of cracks in the dielectric layer
can be reduced and the leakage current can thereby be reduced.
SUMMARY OF THE INVENTION
[0009] The method disclosed in Published Japanese Patent
Application No. 2001-203128 can reduce to a certain extent the
stress transmitted from the anode lead to the dielectric layer in
the molding process by holding the anode lead rigidly as described
above. In the method disclosed in the above document, on the other
hand, in pouring a resin for forming the resin outer package into
the mold for resin molding in the molding process, the resin is
brought into direct contact with a part of the anode lead not
covered with the thermosetting resin. This results in insufficient
reduction of stress transmitted from the anode lead to the
dielectric layer. Furthermore, the other end of the anode lead and
the anode terminal are mechanically fixed to each other only at the
connecting part between them. Therefore, stress due to a pouring
pressure in pouring the resin for forming the resin outer package
is transmitted to the anode terminal, and in turn transmitted to
the anode lead. If in such a case only the root of the anode lead
is rigidly held by a thermosetting resin, the stress applied from
the anode terminal through the anode lead to the dielectric layer
cannot sufficiently be reduced. Accordingly, the method described
in the above document cannot sufficiently suppress the occurrence
of cracks in a part of the dielectric layer located in the vicinity
of the region in which the anode and the anode lead are joined
together, and cannot thereby sufficiently reduce the leakage
current.
[0010] With the foregoing in mind, an object of the present
invention is to provide a solid electrolytic capacitor capable of
reducing the leakage current.
[0011] The present invention is directed to a solid electrolytic
capacitor including at least one capacitor element that includes an
anode, a dielectric layer covering the anode, an electrolyte layer
covering the dielectric layer, a cathode layer partly covering the
electrolyte layer and an anode lead one end of which is joined to
the anode and the other end of which extends beyond an exposed
portion of the electrolyte layer exposed from the cathode layer.
The solid electrolytic capacitor further includes: an anode
terminal connected to the other end of the anode lead, a cathode
terminal connected to the cathode layer, a resin layer and a resin
outer package covering the capacitor element and the resin layer,
wherein the resin layer covering the exposed portion of the
electrolyte layer, the other end of the anode lead, and a
connecting part between the other end of the anode lead and the
anode terminal. The resin layer includes a first resin layer
covering the exposed portion and a second resin layer covering the
first resin layer, the first resin layer being softer than the
second resin layer.
[0012] A described above, in the solid electrolytic capacitor
according to the present invention, a resin layer is formed which
covers the exposed portion, the other end of the anode lead and the
connecting part between the other end of the anode lead and the
anode terminal. In addition, the resin layer includes the first
resin layer and the second resin layer, and the second resin layer
is formed to cover the first resin layer. Therefore, the resin
layer can reduce stress transmitted from the anode terminal through
the anode lead to the dielectric layer in the molding process.
Hence, the occurrence of cracks in the dielectric layer can be
suppressed, and the leakage current can thereby be reduced.
Furthermore, the first resin layer of the solid electrolytic
capacitor according to the present invention is softer than the
second resin layer thereof. Therefore, the first resin layer can
reduce stress applied to the exposed portion of the electrolyte
layer, and the second resin layer can mechanically reinforce the
first resin layer to enhance the stress reduction effect of the
first resin layer. Hence, the occurrence of cracks in a part of the
dielectric layer in the vicinity of the exposed portion can be
suppressed, and the leakage current can thereby be reduced.
[0013] In the present invention, the other end of the anode lead
and the anode terminal may be connected to each other through a
connecting member, and a connecting part between the other end of
the anode lead and the connecting member may be covered with the
resin layer.
[0014] In the present invention, the first resin layer preferably
covers substantially the entire surface of the exposed portion.
[0015] In the present invention, a third resin layer is preferably
formed to cover the cathode layer.
[0016] In the present invention, the penetration of the first resin
layer is preferably within the range of 30 to 200.
[0017] The resin layer preferably covers a connecting part between
the connecting member and the anode terminal. Thus, the stress
transmitted from the anode terminal through the connecting member
and the anode lead to the dielectric layer in the molding process
can be further reduced. This suppresses the occurrence of cracks in
the dielectric layer and thereby further reduces the leakage
current.
[0018] According to the present invention, a solid electrolytic
capacitor capable of reducing the leakage current can be
provided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a cross-sectional view for illustrating a solid
electrolytic capacitor according to a first embodiment.
[0020] FIG. 2 is a cross-sectional view for illustrating a
capacitor element in the first embodiment.
[0021] FIG. 3 shows cross-sectional views for illustrating the
relative positions of first and second resin layers in the first
embodiment.
[0022] FIG. 4 is a cross-sectional view for illustrating a solid
electrolytic capacitor according to Modification 1 of the first
embodiment.
[0023] FIG. 5 is a cross-sectional view for illustrating a solid
electrolytic capacitor according to Modification 2 of the first
embodiment.
[0024] FIG. 6 is a cross-sectional view for illustrating a solid
electrolytic capacitor according to a second embodiment.
[0025] FIG. 7 is a cross-sectional view for illustrating a solid
electrolytic capacitor according to a third embodiment.
[0026] FIG. 8 shows cross-sectional views for illustrating a solid
electrolytic capacitor according to a fourth embodiment.
[0027] FIG. 9 is a cross-sectional view for illustrating a solid
electrolytic capacitor according to Modification 1 of the fourth
embodiment.
[0028] FIG. 10 is a cross-sectional view taken along the line D-D
of FIG. 9.
[0029] FIG. 11 is a cross-sectional view for illustrating a solid
electrolytic capacitor according to Modification 2 of the fourth
embodiment.
[0030] FIG. 12 shows cross-sectional views for illustrating a
process for producing a solid electrolytic capacitor according to
Example 1.
[0031] FIG. 13 is a cross-sectional view for illustrating solid
electrolytic capacitors according to Reference Examples 1 to
10.
[0032] FIG. 14 is a cross-sectional view for illustrating a solid
electrolytic capacitor according to Reference Example 23.
[0033] FIG. 15 is a cross-sectional view for illustrating a solid
electrolytic capacitor according to Reference Example 24.
[0034] FIG. 16 is a cross-sectional view for illustrating a solid
electrolytic capacitor according to Reference Example 25.
[0035] FIG. 17 is a cross-sectional view for illustrating a
conventional solid electrolytic capacitor.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0036] Next, embodiments of the present invention will be described
with reference to the drawings. Throughout the drawings described
below, the same or like reference numerals refer to the same or
like parts. However, it should be noted that each drawing is a
schematic view and may represent different dimensional ratios and
the like from those of the actual solid electrolytic capacitor.
Therefore, specific dimensions and the like should be determined in
consideration of the following descriptions. Furthermore, it is a
matter of course that different drawings include elements which
have different dimensional relations and ratios.
First Embodiment
[0037] FIG. 1 is a schematic cross-sectional view for illustrating
the interior of a solid electrolytic capacitor according to this
embodiment.
[0038] A solid electrolytic capacitor 20 according to this
embodiment has the outer shape of a rectangular box. The solid
electrolytic capacitor 20, as shown in FIG. 1, basically includes a
capacitor element 6, an anode terminal 7, a cathode terminal 9, a
resin outer package 11, and a resin layer 10 composed of a first
resin layer 10a and a second resin layer 10b. These elements will
be described below in an orderly sequence.
[0039] The capacitor element 6 includes an anode 1 made of a valve
metal, an anode lead 2 provided so that its one end 2a is joined to
the anode 1 and the other end 2b extends from the anode 1, a
dielectric layer 3 formed by anodizing the anode 1, an electrolyte
layer 4 covering the dielectric layer 3, and a cathode layer 5
covering the electrolyte layer 4.
[0040] The anode 1 is formed of a porous body made by pressing a
large number of metal particles made of a valve metal into the
shape of an anode and sintering it. One end 2a of the anode lead 2
made of a valve metal is embedded in the anode 1 so that the anode
1 and the anode lead 2 are joined together. The material used for
the anode lead 2 may be the same metal as or a different valve
metal from that for the anode 1. Examples of the valve metal
forming the anode 1 and the anode lead 2 include niobium (Nb),
tantalum (Ta), aluminum (Al) and titanium (Ti). Alternatively, an
alloy containing one of the above valve metals as a main ingredient
may be used for the anode 1 and/or the anode lead 2.
[0041] The dielectric layer 3 can be formed to cover the anode 1 by
anodizing the anode 1. FIG. 1 shows the dielectric layer 3 made of
an oxide layer formed on the outer surface of the anode 1. However,
in actuality, since the anode 1 is a porous body as described
above, the dielectric layer 3 is also formed on the wall surfaces
of the pores in the porous body.
[0042] The electrolyte layer 4 is formed to cover the dielectric
layer 3. An example of a material that can be used for the
electrolyte layer 4 is a conductive polymer formed by chemical
polymerization, electrolytic polymerization or like method. The
electrolyte layer 4 may be formed of a single layer or formed of a
plurality of layers. Typical materials for the conductive polymer
include polypyrrole, polythiophene, polyaniline and polyfuran. FIG.
1 shows the electrolyte layer 4 formed on the dielectric layer 3
formed on the outer surface of the anode 1. However, the
electrolyte layer 4 is also formed on the surface of part of the
dielectric layer 3 formed on the wall surfaces of the pores in the
porous body.
[0043] The cathode layer 5 is formed to partly cover the
electrolyte layer 4, and has a layered structure in which a carbon
layer 5a and a silver paste layer 5b are sequentially formed on the
electrolyte layer 4. In this embodiment, the electrolyte layer 4
has an exposed portion 40 exposed from the cathode layer 5 in the
vicinity of the other end 2b of the anode lead 2. The cathode layer
5 is not formed in the vicinity of the other end 2b of the anode
lead 2 to prevent a short circuit with the anode lead 2. The carbon
layer 5a is formed of a layer containing carbon particles. The
silver paste layer 5b formed on the carbon layer 5a is formed of a
layer containing silver particles.
[0044] FIG. 2 is a perspective view of the capacitor element 6 when
removed out of the solid electrolytic capacitor 20. As shown in
FIG. 2, the electrolyte layer 4 has the exposed portion 40 exposed
from the cathode layer 5, and the other end 2b of the anode lead
extends from the exposed portion 40. Specifically, the electrolyte
layer 4 has the exposed portion 40 exposed from the cathode layer 5
in a surface 50 of the capacitor element 6 that is a surface from
which the other end 2b of the anode lead extends. Note that the
cathode layer 5 may have any other structure that functions as a
cathode.
[0045] The anode terminal 7 is attached to the anode lead 2.
Specifically, the anode terminal 7 is formed by bending a metal
strip. As shown in FIG. 1, the underside of one end 7a of the anode
terminal 7 is mechanically and electrically connected to the other
end 2b of the anode lead by welding or other means. The region a
within the dashed circle in FIG. 1 indicates the connecting part
between the anode lead and the anode terminal 7. This part is
hereinafter referred to as a connecting part .alpha..
[0046] The cathode terminal 9 is attached to the cathode layer 5.
Specifically, the cathode terminal 9 is formed by bending a metal
strip. As shown in FIG. 1, the underside of one end 9a of the
cathode terminal 9 is bonded to the cathode layer 5 by a conductive
adhesive 8, whereby the cathode terminal 9 and the cathode layer 5
are mechanically and electrically connected to each other. A
specific example of a material for the conductive adhesive 8 is a
silver paste made by mixing silver and epoxy resin.
[0047] Examples of materials for the anode terminal 7 and the
cathode terminal 9 include copper, copper alloys and iron-nickel
alloy (42 alloy).
[0048] Next, the resin layer 10 will be described. The structure of
the resin layer 10 will be described below in detail with reference
to FIG. 1 as well as FIG. 3. FIG. 3 shows schematic views for
illustrating the relative positions of the first and second resin
layers 10a and 10b forming the resin layer 10.
[0049] As shown in FIG. 1, in this embodiment, the exposed portion
40, the other end 2b of the anode lead 2 and the connecting part
.alpha. are covered with the resin layer 10. Specifically, the
first resin layer 10a is formed to cover part of the exposed
portion 40, extend from a part of the anode lead sticking out
beyond the electrolyte layer 4 along the other end 2b thereof to
the connecting part .alpha. and also cover the connecting part
.alpha.. The second resin layer 10b is formed to cover the first
resin layer 10a.
[0050] FIG. 3(a) shows the positions of the first and second resin
layers 10a and 10b arranged in a region shown by the surface 50 of
the capacitor element when viewed in the direction of the arrow A
of FIG. 1. Referring to the figure, the first resin layer 10a
arranged within a region shown in the dash-single-dot line covers a
surrounding part of the other end 2b of the anode lead 2 within the
exposed portion 40, and partly covers the exposed portion 40 at
which the electrolyte layer 4 is exposed. The second resin layer
10b arranged within a region shown in the dash-double-dot line is
formed around the first resin layer 10a, and formed to fully cover
the remaining part of the exposed portion 40 in which no first
resin layer 10a exists and reach the cathode layer 5.
[0051] FIG. 3(b) is a view of the solid electrolytic capacitor
according to this embodiment when viewed in the direction of the
arrow B of FIG. 1. Note that the overlapped parts of the anode lead
2, the second resin layer 10b and the anode terminal 7 are shown in
the broken lines or the dash-single-dot line. FIG. 3(c) is a
cross-sectional view taken along the line X-X of FIG. 3(b). Note
that in FIGS. 3(b) and 3(c) the resin outer package 11 is not
given. Referring to FIG. 3(b), the first resin layer 10a is formed
to cover the exposed portion 40, extend from the exposed portion 40
along the other end 2b of the anode lead 2 to the connecting part
.alpha. and cover the connecting part .alpha., and the second resin
layer 10b covers the first resin layer 10a. Furthermore, referring
to FIG. 3(c), the first resin layer 10a is formed to cover the
connecting part .alpha. that is a part at which the strip-shaped
anode terminal 7 is connected to the other end 2b of the anode lead
2. The first resin layer 10a thus formed is adhesively bonded to a
part of the exposed portion 40, the other end 2b of the anode lead
2 and the anode terminal 7. The second resin layer 10b is
adhesively bonded not only to the first resin layer 10a but also to
another part of the exposed portion 40, a part of the cathode layer
5 formed in the surface 50 of the capacitor element 6, and the
anode terminal 7.
[0052] Materials that can be used as the first and second resin
layers 10a and 10b include various kinds of insulating resins, such
as silicon resin and epoxy resin. In this case, the first resin
layer 10a is softer than the second resin layer 10b. Specifically,
the penetration of the first resin layer 10a is greater than that
of the second resin layer 10b. The penetration is a characteristic
representing the resin hardness. The greater its numerical value,
the softer the resin.
[0053] The resin outer package 11 is formed to cover the
surroundings of the capacitor element 6, the anode terminal 7, the
cathode terminal 9 and the second resin layer 10b that are arranged
in the above manner. The other end 7b of the anode terminal 7 and
the other end 9b of the cathode terminal 9 are exposed from the
resin outer package 11 to extend from its side surfaces to its
bottom surface. The exposed portions of the terminals 7 and 9 can
be used for soldering to a substrate. Examples of materials that
can be used for the resin outer package 11 include materials
functioning as sealants. Specific examples of such materials
include epoxy resin and silicon resin. The resin outer package 11
can be formed by curing a resin prepared by appropriately mixing a
base resin, a hardener and a filler.
FUNCTIONS AND EFFECTS
[0054] In the solid electrolytic capacitor 20 according to this
embodiment, the exposed portion 40, the other end 2b of the anode
lead 2 and the connecting part .alpha. are covered with a resin
layer 10 composed of first and second resin layers 10a and 10b.
Since the other end 2b of the anode lead 2 is covered with the
resin layer 10, it can be prevented that in the molding process the
resin for forming the resin outer package 11 comes into direct
contact with the other end 2b of the anode lead 2. Therefore,
transmission of stress generated by a pouring pressure through the
anode lead 2 to the dielectric layer 3 can be suppressed. In
addition, even if the stress generated by a pouring pressure is
transmitted to the anode terminal 7 having a large surface area,
the resin layer 10 formed from around the other end 2b of the anode
lead 2 to around the connecting part .alpha. can suppress
transmission of the stress from the anode terminal 7 through the
anode lead 2 to the dielectric layer 3. Therefore, in the solid
electrolytic capacitor 20 according to this embodiment, the
occurrence of cracks in the dielectric layer 3 can be suppressed,
and the leakage current can thereby be reduced.
[0055] Furthermore, the first resin layer 10a of the solid
electrolytic capacitor 20 according to this embodiment is softer
than the second resin layer 10b thereof. Therefore, the first resin
layer 10a can reduce stress applied to the exposed portion 40 of
the electrolyte layer 4, and the second resin layer 10b can
mechanically reinforce the first resin layer 10a to enhance the
stress reduction effect of the first resin layer 10a on the exposed
portion 40. As a result, the occurrence of cracks in the dielectric
layer 3 can be suppressed, and the leakage current can thereby be
reduced.
[0056] In addition, the connecting part .alpha. of the solid
electrolytic capacitor 20 according to this embodiment is covered
with the first resin layer 10a softer than the second resin layer
10b. Therefore, stress applied to the connecting part .alpha. in
the molding process can be reduced, which further suppresses the
stress transmitted from the anode terminal 7 through the anode lead
2 to the dielectric layer 3.
[0057] In this embodiment, after the connection between the anode
lead 2 and the anode terminal 7 and before the formation of the
resin outer package 11, the first resin layer 10a is formed on the
exposed portion 40 and from around the other end 2b of the anode
lead 2 to around the connecting part .alpha., and the second resin
layer 10b is formed to cover the first resin layer 10a. Therefore,
the anode lead 2, the anode terminal 7 and the capacitor element 6
are rigidly held by the resin layer 10 prior to the molding
process. Thus, the stress transmitted from the anode terminal 7
through the anode lead 2 to the dielectric layer 3 in the molding
process can be reduced. Accordingly, the occurrence of cracks in
the dielectric layer 3 can be suppressed, and the leakage current
can thereby be reduced.
[0058] (Modification 1 of First Embodiment)
[0059] Next will be described below a solid electrolytic capacitor
25 according to Modification 1 of the first embodiment. Note that
the following description is made mainly of the formation of a
third resin layer 13, which is a difference from the above
described first embodiment.
[0060] FIG. 4 is a cross-sectional view for schematically
illustrating the interior of the solid electrolytic capacitor 25
according to this modification.
[0061] As shown in FIG. 4, in this modification, a third resin
layer 13 covers surfaces 51 of the capacitor element 6 in which the
cathode layer 5 is formed. Note that the third resin layer 13 is
adhesively bonded not only to the surfaces 51 of the capacitor
element 6 but also to the cathode terminal 9.
[0062] Materials that can be used for the third resin layer include
various kinds of insulating resins, such as silicon resin and epoxy
resin. Preferably, the third resin layer 13 is made of a softer
resin than the resin outer package 11.
[0063] In the above manner, the surfaces 51 of the capacitor
element 6, at which the cathode layer 5 is exposed with the anode
and cathode terminals 7 and 9 connected to the capacitor element 6,
are further covered with the third resin layer 13. Thus,
application of stress during formation of the resin outer package
11 to the entire dielectric layer 3 can be suppressed. If the third
resin layer 13 is softer than the resin outer package 11,
application of the above stress to the dielectric layer 3 can be
further suppressed.
[0064] Furthermore, the third resin layer 13 is adhesively bonded
to the capacitor element 6 to encapsulate the portion of the
cathode terminal 9 connected with the cathode layer 5 and an
adjacent portion thereof. This prevents the resin outer package 11
from entering the bonding surface between the cathode terminal 9
and the capacitor element 6 in the molding process, thereby
preventing decrease in adhesive strength.
[0065] (Modification 2 of First Embodiment)
[0066] Next will be described below a solid electrolytic capacitor
26 according to Modification 2 of the first embodiment. Note that
the following description is made mainly of the formation of a
fourth resin layer 14, which is a difference from the above
described Modification 1 of the first embodiment.
[0067] FIG. 5 is a cross-sectional view for schematically
illustrating the interior of the solid electrolytic capacitor 26
according to this modification. As shown in the figure, in this
modification, a forth resin layer 14 is formed around the root 2c
of the anode lead 2, which is a part at which the anode lead 2
extends from the surface 50 of the capacitor element 6.
[0068] Materials that can be used for the fourth resin layer 14
include various kinds of insulating resins, such as epoxy resin,
silicon resin and fluorine-contained resin. Preferably, the fourth
resin layer 14 is made of a harder resin than the first resin layer
10a.
[0069] A clearance is likely to be created between the dielectric
layer 3 and the anode lead 2 in the vicinity of the root 2c of the
anode lead 2. Therefore, by covering the root 2c of the anode lead
with the forth resin layer 14, such a clearance can be filled in to
reinforce the root 2c of the anode lead. Thus, the fourth resin
layer 14 restrains the anode lead 2 from being moved by stress
generated in the molding process. This suppresses the occurrence of
cracks in a part of the dielectric layer 3 in the vicinity of the
root 2c of the anode lead and thereby further reduces the leakage
current. If the fourth resin layer 14 is made of a harder resin
than the first resin layer 10a, the above reinforcing effect can be
enhanced.
Second Embodiment
[0070] Next will be described below a solid electrolytic capacitor
21 according to a second embodiment. Note that the following
description is made mainly of the formation of a resin layer 10,
which is a difference from the above described first
embodiment.
[0071] FIG. 6 is a cross-sectional view for schematically
illustrating the interior of the solid electrolytic capacitor 21
according to this embodiment. Also in this embodiment, the exposed
portion 40, the other end 2b of the anode lead 2 and the connecting
part .alpha. are covered with a resin layer 10.
[0072] As shown in the figure, a first resin layer 10a is formed to
cover the connecting part .alpha., then extend around the anode
lead 2 and then cover the entire surface of the exposed portion 40.
A second resin layer 10b is formed to cover the first resin layer
10a, fully cover the surface 50 of the capacitor element and lie
partly on other surfaces of the capacitor element beyond the
surface 50.
[0073] This structure also performs the same effects as in the
first embodiment.
[0074] In addition, in this embodiment, the entire surface of the
exposed portion 40 is covered with the first resin layer 10a softer
than the second resin layer 10b.
Thus, the first resin layer 10a can further reduce the stress
applied to the exposed portion 40 of the electrolyte layer 4.
Third Embodiment
[0075] Next will be described below a solid electrolytic capacitor
22 according to a third embodiment. Note that the following
description is made mainly of the formation of a resin layer 10,
which is a difference from the previously described first
embodiment.
[0076] FIG. 7 is a cross-sectional view for schematically
illustrating the interior of the solid electrolytic capacitor 22
according to this embodiment.
[0077] As shown in the figure, a first resin layer 10a is formed on
part of the exposed portion 40 and around part of the other end 2b
of the anode lead 2, but does not exist around the connecting part
.alpha.. Instead of this, a second resin layer 10b is formed to
cover the connecting part .alpha. and cover substantially the
entire surface of the exposed portion 40.
[0078] Although this embodiment has the above structure, part of
the exposed portion 40 is covered with the first resin layer 10a
softer than the second resin layer 10b.
[0079] Therefore, the first resin layer 10a can reduce the stress
applied to the exposed portion 40 of the electrolyte layer 4.
Fourth Embodiment
[0080] Next will be described below a solid electrolytic capacitor
30 according to a fourth embodiment. Note that the following
description is made mainly of the placement of two capacitor
elements, i.e., first and second capacitor elements 6A and 6B, in
the solid electrolytic capacitor and the formation of a resin layer
10, which are differences from the previously described first
embodiment. The first capacitor element 6A and the second capacitor
element 6B are formed in the same manner as the capacitor element 6
in the first embodiment.
[0081] FIG. 8(a) is a cross-sectional view for schematically
illustrating the interior of the solid electrolytic capacitor 30
according to this embodiment. As shown in this figure, in this
embodiment, the first and second capacitor elements 6A and 6B are
placed pairwise in the solid electrolytic capacitor 30. FIG. 8(b)
is a cross-sectional view taken along the line C-C of FIG. 8(a).
Note that in FIG. 8(b) the resin outer package 11 is not given.
[0082] The top side of one end 7a of the anode terminal 7 is
connected to the other end 2b of the anode lead 2 of the first
capacitor element 6A through a first connecting member 12A
described hereinafter. The underside of the one end 7a of the anode
terminal 7 is connected to the other end 2b of the anode lead 2 of
the second capacitor element 6B through a second connecting member
12B described hereinafter. In this embodiment, as shown in the
above figures, a connecting part .alpha.1 refers to a part at which
the other end 2b of the anode lead 2 of the first capacitor element
6A is connected to the first connecting member 12A, and a
connecting part .alpha.2 refers to a part at which the other end 2b
of the anode lead 2 of the second capacitor element 6B is connected
to the second connecting member 12B. The connection of these
members may be made by welding or with a conductive adhesive.
[0083] The material for the connecting members 12A and 12B may be
any material exhibiting electrical conductivity. Examples of the
material include metallic materials and conductive adhesives.
Various shapes of the connecting members 12A and 12B may be
employed, such as a pillar shape or a plate-like shape. If the
connecting members are made of a metallic material, the metallic
material may be the same material as the anode leads or may be the
same material as the anode terminal. Alternatively, the anode
terminal 7 may be directly connected to the anode leads 2, for
example, by bending or deforming parts of the anode leads 2 and
connecting them to the anode terminal 7. In such a case, the parts
of the anode leads 2 connected to the anode terminal 7 function as
connecting members. Alternatively, the anode terminal 7 may be
directly connected to the anode leads 2, for example, by bending or
deforming parts of the anode terminal 7 and connecting them to the
anode leads 2. In such a case, the parts of the anode terminal 7
connected to the anode leads 2 function as connecting members.
[0084] The top side of one end 9a of the cathode terminal 9 is
connected to the underside of the cathode layer 5 of the first
capacitor element 6A by a conductive adhesive 8. The underside of
the one end 9a of the cathode terminal 9 is connected to the top
side of the cathode layer 5 of the second capacitor element 6B by a
conductive adhesive 8.
[0085] A first resin layer 10a is, as shown in FIG. 8(a), formed to
cover the exposed portion 40 of the first capacitor element 6A,
then extend from the exposed portion 40 along the anode lead 2 and
then cover the connecting part .alpha.1, and formed to cover the
exposed portion 40 of the second capacitor element 6B, then extend
from the exposed portion 40 along the anode lead 2 and then cover
the connecting part .alpha.2. In this embodiment, as shown in FIGS.
8(a) and 8(b), the first resin layer 10a is formed not only around
the connecting parts .alpha.1 and .alpha.2 but also around the
connecting members 12A and 12B and around the region in which the
end 7a of the anode terminal 7 is connected to the connecting
members 12A and 12B. Note that in this embodiment the first resin
layer 10a is integrally formed from the first capacitor element 6A
to the second capacitor element 6B, a first resin layer 10a on the
first capacitor element 6A and a first resin layer 10a on the
second capacitor element 6B may be formed separately.
[0086] As shown in FIGS. 8(a) and 8(b), a second resin layer 10b is
provided to cover the first resin layer 10a provided around the
connecting parts .alpha.1 and .alpha.2. Furthermore, the second
resin layer 10b is adhesively bonded not only to the first resin
layer 10a but also to the surfaces 50 of the capacitor elements 6A
and 6B and the anode terminal 7. Like the first resin layer 10a,
the second resin layer 10b is integrally formed from the first
capacitor element 6A to the second capacitor element 6B. However, a
second resin layer 10b on the first capacitor element 6A and a
second resin layer 10b on the second capacitor element 6B may be
formed separately.
[0087] Such a solid electrolytic capacitor including two capacitor
elements 6A and 6B can also perform the same effects as in the
previously described embodiments, if a resin layer 10 composed of a
first resin layer 10a and a second resin layer 10b is formed as
described above.
[0088] Furthermore, if, in the case of the cathode terminal 9
connected between the first and second capacitor elements 6A and 6B
like this embodiment, the resin layer 10 is integrally formed from
the first capacitor element 6A to the second capacitor element 6B,
this prevents the resin outer package 11 from entering the bonding
surfaces of the cathode terminal 9 to the first and second
capacitor elements 6A and 6B through the surfaces 50 of the
capacitor elements, and thereby prevents decrease in adhesive
strength.
[0089] In this embodiment, the first and second capacitor elements
6A and 6B are arranged to be stacked vertically with respect to the
bottom surface of the solid electrolytic capacitor 30 having the
other end 7b of the anode terminal and the other end 9b of the
cathode terminal, which are parts to be mounted on a substrate.
However, the arrangement of the capacitor elements are not limited
to this and various arrangements can be employed. For example, two
capacitor elements may be horizontally aligned in parallel with the
bottom surface of the solid electrolytic capacitor 30. In this
embodiment, the resin layer 10 is formed on both the first and
second capacitor elements 6A and 6B. However, the resin layer 10
may be formed only on one of the first and second capacitor
elements 6A and 6B.
[0090] Furthermore, even if the solid electrolytic capacitor
includes a single capacitor element, the anode lead 2 and the anode
terminal 7 may be connected to each other through a connecting
member.
[0091] (Modification 1 of Fourth Embodiment)
[0092] Next will be described below a solid electrolytic capacitor
31 according to Modification 1 of the fourth embodiment. Note that
the following description is made mainly of the formation of a
third resin layer 13, which is a difference from the above
described fourth embodiment.
[0093] FIG. 9 is a cross-sectional view for schematically
illustrating the interior of the solid electrolytic capacitor 31
according to this modification. FIG. 10 is a cross-sectional view
taken along the line D-D of FIG. 9.
[0094] As shown in FIGS. 9 and 10, in this modification, a third
resin layer 13 covers the surfaces 51 of the first and second
capacitor elements 6A and 6B, except for the surfaces 50 of the
capacitor elements 6A and 6B, the under surface of the first
capacitor element 6A connected with the cathode terminal 9 and the
top surface of the second capacitor element 6B connected with the
cathode terminal 9. Note that the third resin layer 13 is
adhesively bonded not only to the surfaces 51 of the capacitor
elements 6A and 6B but also to the cathode terminal 9.
[0095] Materials that can be used for the third resin layer include
various kinds of insulating resins, such as silicon resin and epoxy
resin. Preferably, the third resin layer 13 is made of a softer
resin than the resin outer package 11.
[0096] In the above manner, the surfaces 51 of the capacitor
elements 6A and 6B, at which the cathode layers 5 are exposed with
the anode and cathode terminals 7 and 9 connected to the capacitor
elements 6A and 6B, are further covered with the third resin layer
13. Thus, application of stress during formation of the resin outer
package 11 to the entire dielectric layers 3 can be suppressed. If
the third resin layer 13 is softer than the resin outer package 11,
application of the above stress to the dielectric layers 3 can be
further suppressed.
[0097] Furthermore, the third resin layer 13 is adhesively bonded
also to the cathode terminal 9. This prevents the resin outer
package 11 from entering the bonding surfaces of the cathode
terminal 9 to the first and second capacitor elements 6A and 6B in
the molding process, thereby preventing decrease in adhesive
strength.
[0098] (Modification 2 of Fourth Embodiment)
[0099] Next will be described below a solid electrolytic capacitor
32 according to Modification 2 of the fourth embodiment. Note that
the following description is made mainly of the formation of fourth
resin layers 14, which is a difference from the above described
Modification 1 of the fourth embodiment.
[0100] FIG. 11 is a cross-sectional view for schematically
illustrating the interior of the solid electrolytic capacitor 32
according to this modification. As shown in the figure, in this
modification, a forth resin layer 14 is formed around each of the
roots 2c of the anode leads 2, which are parts at which the anode
leads 2 extend from the surfaces 50 of the capacitor elements 6A
and 6B.
[0101] Materials that can be used for the fourth resin layers 14
include various kinds of insulating resins, such as epoxy resin,
silicon resin and fluorine-contained resin. Preferably, the fourth
resin layers 14 are made of a harder resin than the first resin
layer 10a.
[0102] A clearance is likely to be created between each dielectric
layer 3 and the associated anode lead 2 in the vicinity of the root
2c of the anode lead 2 during bonding between the dielectric layer
3 and the anode lead 2. Therefore, by covering the root 2c of each
anode lead with the forth resin layer 14, such a clearance can be
filled in to reinforce the root 2c of the anode lead. Thus, the
fourth resin layers 14 restrain the anode leads 2 from being moved
by stress generated in the molding process. This suppresses the
occurrence of cracks in parts of the dielectric layers 3 in the
vicinity of the roots 2c of the anode leads and thereby further
reduces the leakage current. If the fourth resin layers 14 are made
of a harder resin than the first resin layer 10a, the above
reinforcing effect can be enhanced.
Example 1
[0103] Hereinafter will be described Example 1 in which niobium is
used for the anode in the solid electrolytic capacitor according to
the first embodiment.
[0104] FIG. 12 shows views illustrating a process for producing a
solid electrolytic capacitor according to Example 1.
[0105] <Step 1: Formation of Anode>
[0106] As shown in FIG. 12(a), valve metal powder made of niobium
metal and having a primary particle size of approximately 0.5 .mu.m
was pressed into the shape of an anode 1 with one end 2a of an
anode lead 2 embedded therein, and sintered in vacuum, thereby
forming an anode 1. Thus, the other end 2b of the anode lead 2 was
fixed in a state extended from one surface of the anode 2. The
anode 1 made of a porous sintered body thus formed had the outer
shape of a rectangular box with a length of 4.4 mm in the direction
of extension of the anode lead 2, a width of 3.3 mm and a thickness
of 1.0 mm.
[0107] Although niobium was used for the anode in this example,
various kinds of valve metals, such as tantalum, and their alloys
can be used for the anode. A dielectric layer formed by using
niobium as an anode material and anodizing it is more likely to
cause oxygen diffusion and defects and therefore more likely to
increase the leakage current than a dielectric layer formed by
using tantalum as an anode material and anodizing it. Therefore,
the effects of the invention are most desired for solid
electrolytic capacitors using niobium as their anodes. Such a solid
electrolytic capacitor was produced as this example and examined as
described below.
[0108] <Step 2: Formation of Dielectric Layer>
[0109] As shown in FIG. 12(b), a dielectric layer 3 formed of an
oxide layer was formed on the surface of the anode 1 by anodizing
the anode 1. Specifically, anodization was implemented by immersing
the anode 1 in an approximately 0.1% by weight aqueous solution of
ammonium fluoride held at approximately 40.degree. C. and applying
a constant voltage of approximately 10 V to the anode 1 for
approximately ten hours. Thereafter, another anodization was
implemented by immersing the anode 1 in a 0.5% by weight aqueous
solution of phosphoric acid and applying a constant voltage of
approximately 10 V to the anode 1 for approximately two hours,
thereby forming a dielectric layer 3 containing fluorine.
[0110] <Step 3: Formation of Electrolyte Layer>
[0111] As shown in FIG. 12(c), an electrolyte layer 4 made of
polypyrrole was formed on the surface of the dielectric layer 3 by
chemical polymerization or other methods.
[0112] <Step 4: Formation of Cathode Layer>
[0113] As shown in FIG. 12(d), a carbon layer 5a was formed by
applying carbon paste on the surface of the electrolyte layer 4 and
drying it, and a silver paste layer 5b was then formed by applying
silver paste on the carbon layer 5a and drying it. In this example,
the cathode layer 5 was composed of the carbon layer 5a and the
silver paste layer 5b.
[0114] Through the above Steps 1 to 4, a capacitor element 6 was
formed. The outer shape of the capacitor element 6 thus formed
(exclusive of the extension of the anode lead 2b) was a rectangular
box shape like the outer shape of the anode 1, because the
dielectric layer 3, the electrolyte layer 4 and the cathode layer 5
all formed on the anode 1 had small thicknesses. The cathode layer
was coated on, out of all the surfaces forming the rectangular box,
five surfaces of the capacitor element other than the surface 50.
Therefore, an exposed portion 40 of the electrolyte layer 4 exposed
from the cathode layer 5 was formed in the surface 50 of the
capacitor element.
[0115] <Step 5: Connection of Anode Terminal and Cathode
Terminal>
[0116] As shown in FIG. 12(e), an end 7a of an anode terminal 7 was
electrically and mechanically connected to an end 2b of the anode
lead 2 by welding or other means. The end 2b of the anode lead 2
and the end 7a of the anode terminal 7 were connected at a
connecting part .alpha. as shown in the figure. Furthermore, an end
9a of a cathode terminal 9 was electrically and mechanically
connected to a surface of the cathode layer 5 by a conductive
adhesive 8.
[0117] <Step 6: Formation of Resin Layer 10 Composed of First
Resin Layer 10a and Second Resin Layer 10b>
[0118] As shown in FIG. 12(f), a first resin layer 10a made of
silicon resin was formed to cover the connecting part .alpha.,
which is a part at which the anode terminal 7 and the anode lead
were connected to each other in Step 5, continue from the
connecting part .alpha. along the anode lead to the exposed portion
40 and cover part of the exposed portion 40. Next, a second resin
layer 10b made of silicon resin was formed to entirely cover the
first resin layer 10a and the exposed portion 40.
[0119] Specifically, the silicon resin used was Part No. TSE3070
manufactured by Momentive Performance Materials Japan LLC. To form
the first resin layer 10a, 100 parts by weight of solution of
TSE3070(A) was blended with 100 parts by weight of solution of
TSE3070(B) and the blended solution was uniformly stirred to
prepare a resin. Thereafter, the resin was applied with a dispenser
to cover the specific parts described above and cured at 70.degree.
C. for 30 minutes, thereby forming a first resin layer 10a made of
silicon resin. The penetration of the first resin layer 10a thus
formed was measured according to JIS K6249. The measured
penetration was 65.
[0120] To form the second resin layer 10b, 100 parts by weight of
solution of TSE3070(A) was blended with 130 parts by weight of
solution of TSE3070(B) and the blended solution was uniformly
stirred to prepare a resin. Thereafter, the resin was applied with
a dispenser to cover the specific parts described above and cured
at 70.degree. C. for 30 minutes, thereby forming a second resin
layer 10b made of silicon resin. The penetration of the second
resin layer 10b thus formed was measured according to JIS K6249.
The measured penetration was 15.
[0121] A resin layer 10 was formed by sequentially forming the
first and second resin layers 10a and 10b in the above manner.
[0122] Note that the penetration is a characteristic representing
the resin hardness, and the greater its numerical value, the softer
the resin.
[0123] <Step 7: Molding Process>
[0124] As shown in FIG. 12(g), the capacitor element 6 subjected to
Steps 1 to 6 was encapsulated by transfer molding with a sealant
containing epoxy resin and an imidazole compound to allow the anode
and cathode terminals to be partly exposed to the outside, thereby
forming a resin outer package 11. Specifically, the sealant
previously heated at 160.degree. C. was poured into a mold under a
pressure of 80 kg/cm.sup.2, and cured in the mold under conditions
of 160.degree. C. for 90 seconds. After the formation of the resin
outer package 11, the exposed parts of the anode and cathode
terminals were bent from the lateral sides of the resin outer
package 11 to the bottom surface thereof, thereby forming terminal
ends 7b and 9b to be used for soldering to a substrate. The
penetration of the resin outer package 11 was below 10.
Reference Examples 1 to 10
[0125] FIG. 13 is a cross-sectional view showing solid electrolytic
capacitors 23 according to Reference Examples 1 to 10 in which the
second resin layer 10b is not formed unlike Example 1. To obtain
the index for selecting a suitable resin material for the first
resin layer 10a to be in contact with the exposed portion 40, the
effect of a solid electrolytic capacitor having only a first resin
layer 10a formed as a resin layer as shown in FIG. 13 was examined
by changing the penetration of the first resin layer 10a. A solid
electrolytic capacitor according to Reference Example 1 was
produced in the same manner as in Example 1, except that the second
resin layer 10b was not formed and the first resin layer 10a was
formed also in a region where the second resin layer 10b should be
formed in Example 1. The exposed portion 40 of the solid
electrolytic capacitor according to this reference example formed
in the above manner was covered with the first resin layer 10a.
[0126] Solid electrolytic capacitors according to Reference
Examples 1 to 10 were obtained by producing them in the above
manner to allow their first resin layers 10a to have different
penetrations of 15, 30, 40, 65, 90, 110, 150, 180, 200 and 220.
[0127] (Measurement of Leakage Current)
[0128] A voltage of 2.5 V was applied to the solid electrolytic
capacitors according to Reference Examples 1 to 10, and their
leakage currents were measured 20 seconds after the voltage
application. TABLE 1 shows the results of leakage current
measurement. Note that the values of leakage current are relative
values when the value of leakage current in Reference Example 1 is
taken as 100.
TABLE-US-00001 TABLE 1 Leakage Blending Ratio Current (Parts by
Weight) (Relative A B Penetration Value) Ref. Ex. 2 100 130 15
155.00 Ref. Ex. 3 100 120 30 121.25 Ref. Ex. 4 100 110 40 106.25
Ref. Ex. 1 100 100 65 100.00 Ref. Ex. 5 100 95 90 102.50 Ref. Ex. 6
100 90 110 106.25 Ref. Ex. 7 100 85 150 112.50 Ref. Ex. 8 100 80
180 120.00 Ref. Ex. 9 100 75 200 125.00 Ref. Ex. 10 100 70 220
160.00
[0129] TABLE 1 shows that in resin layers of single layer
structure, if the penetration of silicon resin used for the first
resin layer 10a was within the range of 30 to 200, the resin layer
could reduce the leakage current as compared to the other
penetrations. Furthermore, it was founded that the penetration
should more preferably be within the range of 40 to 150.
[0130] In view of these findings and based on the results of the
best three of Reference Examples that could reduce the leakage
current, i.e., Reference Examples 1, 4 and 5, solid electrolytic
capacitors according to Examples 2 to 9 were also produced.
Examples 2 and 3
[0131] Solid electrolytic capacitors according to Examples 2 and 3
were produced by conducting Step 6 in Example 1 to bring the
respective penetrations of their second resin layers to 30 and 40.
The formation of silicon resins having different penetrations can
be controlled by changing the blending ratio of solution of
TSE3070(B) to solution of TSE3070(A). Specifically, 100 parts by
weight of solution of TSE3070(A) was blended with each of 120 parts
by weight of solution of TSE3070(B) and 110 parts by weight of
solution of TSE3070(B), thereby forming second resin layers in
Examples 2 and 3, respectively. In producing the solid electrolytic
capacitors according to Examples 2 and 3, the other steps were the
same as in Example 1.
Reference Examples 11 to 14
[0132] Solid electrolytic capacitors according to Reference
Examples 11 to 14 were produced in the same manner as in Example 1
except that in Step 6 in Example 1 silicon resins were used to
bring the respective penetrations of their second resin layers to
65, 90, 180 and 220. Specifically, 100 parts by weight of solution
of TSE3070(A) was blended with each of 100 parts by weight of
solution of TSE3070(B), 95 parts by weight of solution of
TSE3070(B), 80 parts by weight of solution of TSE3070(B) and 70
parts by weight of solution of TSE3070(B), thereby preparing solid
electrolytic capacitors according to Reference Examples 11 to 14,
respectively.
[0133] (Measurement of Leakage Current)
[0134] A voltage of 2.5 V was applied to the solid electrolytic
capacitors according to Examples 1 to 3 and Reference Examples 11
to 14, and their leakage currents were measured 20 seconds after
the voltage application. TABLE 2 shows the results of leakage
current measurement. Note that the values of leakage current are
relative values when the value of leakage current in Reference
Example 1 is taken as 100.
TABLE-US-00002 TABLE 2 Leakage Current Penetration of Penetration
of (Relative First Resin Layer Second Resin Layer Value) Ex. 1 65
15 81.25 Ex. 2 65 30 75.00 Ex. 3 65 40 80.00 Ref. Ex. 11 65 65
100.00 Ref. Ex. 12 65 90 101.25 Ref. Ex. 13 65 180 117.50 Ref. Ex.
14 65 220 156.25
[0135] Examples 1 to 3 could reduce the leakage current as compared
to Reference Examples 11 to 14. The reason for this can be
explained as follows: In Examples 1 to 3, the exposed portion 40,
the other end 2b of the anode lead and the connecting part .alpha.
were covered with a resin layer 10 composed of first and second
resin layers 10a and 10b and, additionally, the first resin layer
10a was softer than the second resin layer 10b. Therefore, in
Examples 1 to 3, stress transmitted from the exposed portion 40 and
the anode lead 2 to the dielectric layer 3 and stress transmitted
from the anode terminal 7 through the anode lead 2 to the
dielectric layer 3 in the molding process could be reduced. Thus,
the occurrence of cracks in the dielectric layer 3 can be
suppressed, and the leakage current could thereby be reduced.
[0136] On the other hand, in Reference Example 11 in which both the
first and second resin layers 10a and 10b were formed but had equal
penetrations and in Reference Examples 12 to 14 in which both the
first and second resin layers 10a and 10b were formed but the
second resin layer 10b had a greater penetration than the first
resin layer 10a, the leakage current could not be reduced. The
reason for this can be explained as follows: In Reference Examples
11 to 14, since the penetration of each second resin layer 10b is
equal to or greater than that of the first resin layer 10a, each of
the second resin layers 10b in Reference Examples 11 to 14 could
not increase the effect of mechanically reinforcing the first resin
layer 10a. Therefore, Reference Examples 11 to 14 could not
increase the effect of the first resin layer 10a reducing the
stress on the exposed portion 40 and, therefore, could not reduce
the stress transmitted from the anode terminal 7 through the anode
lead 2 to the dielectric layer 3, whereby their leakage currents
were increased.
[0137] It can be assumed that, for the reasons described so far,
Examples 1 to 3 could suppress the occurrence of cracks and the
like in the dielectric layer 3 and reduce the leakage current,
unlike Reference Examples 11 to 14.
Examples 4 and 5
[0138] Solid electrolytic capacitors according to Examples 4 and 5
were produced in the same manner as in Example 1, except that in
Step 6 in Example 1 silicon resins were used to bring the
penetration of their first resin layers to 40 and silicon resins
were used to bring the respective penetrations of their second
resin layers to 15 and 30.
Reference Examples 15 to 19
[0139] Solid electrolytic capacitors according to Reference
Examples 15 to 19 were produced in the same manner as in Example 1,
except that in Step 6 in Example 1 silicon resins were used to
bring the penetration of their first resin layers to 40 and silicon
resins were used to bring the respective penetrations of their
second resin layers to 40, 65, 90, 180 and 220.
[0140] TABLE 3 shows the results of leakage current measurement.
Note that the values of leakage current are relative values when
the value of leakage current in Reference Example 1 is taken as
100.
TABLE-US-00003 TABLE 3 Leakage Current Penetration of Penetration
of (Relative First Resin Layer Second Resin Layer Value) Ex. 4 40
15 80.00 Ex. 5 40 30 83.75 Ref. Ex. 15 40 40 106.25 Ref. Ex. 16 40
65 108.75 Ref. Ex. 17 40 90 110.00 Ref. Ex. 18 40 180 122.50 Ref.
Ex. 19 40 220 157.50
[0141] It can be assumed that Examples 4 and 5, unlike Reference
Examples 15 to 19, could suppress the occurrence of cracks and the
like in the dielectric layer 3 for the same reasons as in the
previously stated results (Examples 1 to 3) and, therefore, could
reduce the leakage current.
Examples 6 to 9
[0142] Solid electrolytic capacitors according to Examples 6 to 9
were produced in the same manner as in Example 1, except that in
Step 6 in Example 1 silicon resins were used to bring the
penetration of their first resin layers to 90 and silicon resins
were used to bring the respective penetrations of their second
resin layers to 15, 30, 40 and 65.
Reference Examples 20 to 22
[0143] Solid electrolytic capacitors according to Reference
Examples 20 to 22 were produced in the same manner as in Example 1,
except that in Step 6 in Example 1 silicon resins were used to
bring the penetration of their first resin layers to 90 and silicon
resins were used to bring the respective penetrations of their
second resin layers to 90, 180 and 220.
[0144] TABLE 4 shows the results of leakage current measurement.
Note that the values of leakage current are relative values when
the value of leakage current in Reference Example 1 is taken as
100.
TABLE-US-00004 TABLE 4 Leakage Current Penetration of Penetration
of (Relative First Resin Layer Second Resin Layer Value) Ex. 6 90
15 83.75 Ex. 7 90 30 80.00 Ex. 8 90 40 77.50 Ex. 9 90 65 81.25 Ref.
Ex. 20 90 90 102.50 Ref. Ex. 21 90 180 117.50 Ref. Ex. 22 90 220
155.00
[0145] It can be assumed that Examples 6 to 9, unlike Reference
Examples 20 to 22, could suppress the occurrence of cracks and the
like in the dielectric layer 3 for the same reasons as in the
previously stated results (Examples 1 to 3) and, therefore, could
reduce the leakage current.
[0146] Examples 1 to 9 could reduce the leakage current as compared
to Reference Examples 11 to 22. In Examples 1 to 9, by making the
penetration of the first resin layer 10a greater than that of the
second resin layer 10b, the first resin layer 10a is made
relatively softer than the second resin layer 10b. Therefore,
stress due to a pouring pressure in the molding process can be
reduced by the soft first resin layer 10a. This can reduce the
stress transmitted from the exposed portion 40 and the anode lead 2
to the dielectric layer and the stress transmitted from the anode
terminal 7 through the anode lead 2 to the dielectric layer.
Furthermore, since, in sequentially forming the first and second
resin layers 10a and 10b, the first resin layer 10a is covered with
the second resin layer 10b harder than the first resin layer 10a,
the first resin layer 10a covering the exposed portion 40 can be
stably held by the second resin layer 10b. Thus, the transmission
of stress on the exposed portion 40 to the dielectric layer can be
effectively suppressed. For these reasons, Examples 1 to 9 can
reduce the leakage current as compared to Reference Examples 11 to
22.
[0147] The results of Reference Examples 1 to 10 also shows that
the penetration of resin to be used for the first resin layer 10a
is preferably within the range of 30 to 200. More preferred
penetration of resin to be used for the first resin layer 10a is
within the range of 40 to 150. The reason for this is as follows:
If the penetration of the first resin layer 10a is too small, the
function of reducing the stress on the exposed portion 40 is
decreased. On the other hand, if the penetration of the first resin
layer 10a is too great, the resin becomes too soft, which makes the
resin difficult to handle, makes it difficult for the second resin
layer 10b to hold the first resin layer 10a and in turn decreases
the function of reducing the stress.
Reference Example 23
[0148] FIG. 14 is a cross-sectional view of a solid electrolytic
capacitor 121 according to Reference Example 23.
[0149] In this reference example, a solid electrolytic capacitor
121 according to Reference Example 23 was produced in the same
manner as in Example 1 except that Step 6 in Example 1 was not
conducted, i.e., the resin layer 10 in Example 1 was not
formed.
[0150] TABLE 5 shows the result of leakage current measurement.
Note that the value of leakage current is a relative value when the
value of leakage current in Reference Example 1 is taken as
100.
TABLE-US-00005 TABLE 5 Leakage Current (Relative Value) Ref. Ex. 23
1537.50
[0151] Reference Example 23, in which any resin layer 10 composed
of first and second resin layers 10a and 10b was not formed,
significantly increased the leakage current as compared to Examples
1 to 9. It can be assumed that, in Reference Example 23, since
first and second resin layers 10a and 10b were not formed, stress
transmitted from the anode terminal 7 through the anode lead 2 to
the dielectric layer in the molding process could not be reduced,
whereby the leakage current was increased. In addition, it can be
assumed that, in Reference Example 23, since any resin layer 10 for
protecting the exposed portion was not formed, the leakage current
was increased.
Example 10
[0152] A solid electrolytic capacitor 30 of Example 10 according to
the fourth embodiment was produced. In producing the solid
electrolytic capacitor 30 according to Example 10, the rest of the
process except for the steps described below was the same as in
Example 1.
[0153] In Steps 1 to 4, two capacitor elements 6A and 6B were
formed in the same manner as in Example 1.
[0154] In Step 5, the capacitor elements 6A and 6B were connected
to the anode terminal 7 and the cathode terminal 9. As shown in
FIG. 8, the connection between the top side of one end 7a of the
anode terminal 7 and the other end 2b of the anode lead 2 of the
first capacitor element 6A was made at the connecting part .alpha.1
through a first connecting member 12A. The connection between the
underside of the one end 7a of the anode terminal 7 and the other
end 2b of the anode lead 2 of the second capacitor element 6B was
made at the connecting part .alpha.2 through a second connecting
member 12B. The top side of one end 9a of the cathode terminal 9
was connected to the underside of the first capacitor element 6A by
a conductive adhesive 8. The underside of the one end 9a of the
cathode terminal 9 was connected to the top side of the second
capacitor element 68 by a conductive adhesive 8.
[0155] In Step 6, as shown in FIG. 8, a first resin layer 10a was
formed to cover part of the exposed portion 40, the connecting part
.alpha.1 and the connecting member 12A of the capacitor element 6A,
part of the exposed portion 40, the connecting part .alpha.2 and
the connecting member 12B of the capacitor element 6B, and a part
at which one end 7a of the anode terminal 7 was connected to the
connecting members 12A and 12B. Then, a second resin layer 10b was
formed to cover the first resin layer 10a.
Example 11
[0156] A solid electrolytic capacitor 31 of Example 11 according to
Modification 1 of the fourth embodiment was produced (see FIG. 9).
In producing the solid electrolytic capacitor 31 according to
Example 11, the rest of the process except for the step described
below was the same as in Example 10.
[0157] In Step 6, a first resin layer 10a was formed, a second
resin layer 10b was then formed to cover the first resin layer 10a,
and a third resin layer 13 was formed to cover the surfaces 51 of
the capacitor elements 6A and 6B at which the cathode layers 5 were
exposed with the anode and cathode terminals 7 and 9 connected to
the capacitor elements 6A and 6B. Silicon resin was used for the
third resin layer 13. Specifically, the silicon resin used was Part
No. TSE3253 manufactured by Momentive Performance Materials Japan
LLC. The penetration of the third resin layer 13 thus formed was
15.
Example 12
[0158] A solid electrolytic capacitor 32 according to Example 12
was produced in the same manner as in Example 11 except that a
fourth resin layer 14 was formed around each of the roots 2c of the
anode leads 2, which are parts at which the anode lead 2 extend
from the surfaces 50 of the capacitor elements 6A and 6B subjected
to Steps 1 to 4 (see FIG. 11). Epoxy resin was used for the third
resin layer 10d. Specifically, the epoxy resin used was Part No.
ME-5909 manufactured by Nippon Pelnox Corporation. The penetration
of the third resin layer 10d thus formed was below 10.
Reference Example 24
[0159] FIG. 15 is a cross-sectional view of a solid electrolytic
capacitor 130 according to Reference Example 24.
[0160] In this reference example, a solid electrolytic capacitor
130 according to Reference Example 24 was produced in the same
manner as in Example 10 except that Step 6 in Example 10 was not
conducted, i.e., the resin layer 10 in Example 10 was not
formed.
Reference Example 25
[0161] FIG. 16 is a cross-sectional view of a solid electrolytic
capacitor 131 according to Reference Example 25. In this reference
example, a solid electrolytic capacitor 131 according to Reference
Example 25 was produced in the same manner as in Example 12 except
that Step 6 in Example 12 was not conducted, i.e., the resin layer
10 and the third resin layer 13 in Example 12 were not formed.
[0162] TABLE 6 shows the results of leakage current measurement.
Note that the values of leakage current are relative values when
the value of leakage current in Example 10 is taken as 100.
TABLE-US-00006 TABLE 6 Leakage Current Penetration of Penetration
of (Relative First Resin Layer Second Resin Layer Value) Ex. 10 60
15 100 Ex. 11 60 15 93 Ex. 12 60 15 90 Ref. Ex. 24 -- -- 3129 Ref.
Ex. 25 -- -- 1952
[0163] Examples 10 to 12 could reduce the leakage current as
compared to Reference Examples 24 and 25 in which the resin layer
10 was not formed. It was proved from the results of Examples 11
and 12 that the leakage current can be further reduced by forming
the first resin layer 13 or the fourth resin layer 14.
* * * * *